かろん / Karonの投稿

$$ \boxed{ \begin{aligned} Z(J) &= \int \exp\!\left[ -\int_{\mathbb{R}^4} \left( \frac{1}{2} \partial_\mu\phi\, \partial^\mu\phi + \frac{m^2}{2}\phi^2 + \frac{\lambda}{4!}\phi^4 - J\phi \right) \,d^4x \right] \mathcal{D}\phi,\\[1ex] \langle\phi(x_1)\cdots\phi(x_n)\rangle &= \left. \frac{1}{Z(0)} \frac{\delta^nZ(J)} {\delta J(x_1)\cdots\delta J(x_n)} \right|_{J=0}. \end{aligned} } $$